Computer networks
At what layer are frames defined?
Data link layer
What is the name and number of the second-lowest network standards layer?
Data link layer, Layer 2
When a packet travels through an internet, are there usually more data links or routes along the way?
Data links
When a packet is transmitted from a source host to a destination host separated by 17 single networks, how many packets will there be?
1
When a packet is transmitted from a source host to a destination host separated by four single networks, how many packets will there be?
1
What are 1-bit fields called?
1-bit fields are called flag fields.
Write 0.032 Mbps properly.
32 kbps
Express 47,303,000 bps with a metric prefix.
47.303 Mbps
To what type of device do single networks think they are delivering frames?
A destination host
What device connects different single networks together into an internet?
A router
Under what conditions will a source host TCP process retransmit a segment?
A source host will retransmit a segment if it doesn't receive an ACK segment.
What is VM instantiation?
Creating a new VM.
Who uses this format, 128.171.17.13?
Humans
What kind of address is 128.171.17.13?
IPv4
Describe the simple message ordering in HTTP.
In a HTTP request-response cycle, a client will send a request to a server. When the server receives the request from the client, it will then send a response and the HTTP request-response cycle is complete.
How are these messages carried in single networks?
Inside frames.
Why is the Internet usually depicted as a cloud?
It symbolizes that users should not have to know how it works, just as you do not have to know how the electrical system works when you turn on a light.
At what layer do you find:wire connections
Layer 1
At what layer do you find: switches
Layer 2
At what layer do you find:EUI-48 addresses
Layer 2 (data link)
At what layer do you find:frames
Layer 2 (data link)
At what layer do you find:routers
Layer 3
Who controls the Internet?
No one.
Who owns and manages the applications in IaaSs and SaaSs?
The cloud server provider in SaaS; the customer in IaaS.
Why is the following NOT an EUI-48 address: A9-00-FF-93-BD?
There are only five symbol pairs, not six.
In a hybrid single-switched network, why do wireless clients need to connect to the wired network?
This is where resources are that then need, including servers and the firm's Internet access router.
In 802.11 Wi-Fi networks, what device relays frames between the source and destination hosts?
Wireless access point.
Can you have a mixed wired and wireless network?
Yes
Is there always a single data link for a frame in a single network?
Yes
What concerns do customers have about cloud security?
That critical corporate data in the cloud may be hacked, that the government may be secretly looking at their data
Write 37kbps properly.
37 kbps (needed a space)
When a packet is transmitted from a source host to a destination host separated by four single networks,how many frames will there be?
4
How long are Ethernet EUI-48 addresses?
48 bits long.
How many bits per second is 56 kbps without a metric prefix. (In other words, how many bits per second is it?)
56,000 bps
When a cloud virtual client is used, describe what happens when a user moves from one physical client device to another.
All data files, applications, and application program personalizations are available to them.
What do physical layer standards govern?
Connectors and physical transmission.
At what layer do you find EUI-addresses? (The answer is not directly in the text. It requires you to integrate the information you have learned.)
Data link layer
What does Layer 2 standardize?
Data link layer standards describe the structure of frames, DLL addresses, and how to deliver frames across a single network.
What name do we use for the format 128.171.17.13?
Dotted decimal notation
How does Netflix use AWS?
For transcoding, selecting the best transcoded version for a particular user and set of network conditions, and personalized recommendations.
What two things do 802.11 data link layer standards govern?
Frame organization and access point operation
Is Google an IaaS or a SaaS for Netflix?
Google is a SaaS provider
If the ACK bit is set, what other field must have a value?
If the ACK bit is set, the acknowledgment number field must have a value also. This will indicate the message being acknowledged.
How does fragmentation improve error handling?
If there is a transmission error, only a single frame or packet is resent—not the entire applications message, which can be very long.
Describe the three-step handshake in TCP connection openings.
In the three-step handshake opening, Host A initiates communication with Host B by sending it a TCP SYN segment. When Host B receives the TCP SYN segment, it sends acknowledgement that it was received the TCP SYN segment back to Host A. Host B does this by sending Host A a TCP SYN/ACK segment. When host A receives the TCP SYN/ACK segment from Host B it sends back another acknowledgment that it received the acknowledgment segment. This acknowledgment is called a pure TCP ACK segment. And once this process is complete, a connection has been initiated between Host A and Host B.
What does Layer 3 standardize?
Internet layer standards describe the structure of IP packets, IP addresses, and how to deliver packets across a series of routers in an internet.
What else is EUI-48 called?
MAC address
What can be done with virtual machines that would be difficult to do with physical servers?
Nearly instantaneous setup, tear-down, and movement to another machine.
Give the definition of network standards that this chapter introduced.
Network standards are a set of rules that apply to how messages are exchanged between two hosts.
Do single networks know that they are delivering frames to a router?
No
Ethernet does error detection but not error correction. Is Ethernet a reliable protocol? Explain.
No. Reliability requires not only error detection, which Ethernet does, but also error correction, which Ethernet does not do.
Why are sequence numbers good?
Sequence numbers are good because each segment has a sequence number which allows the receiver to confirm that there are no missing messages, ensures that all duplicate messages are deleted, and it helps to place segments in the correct order.
What is required for competition among vendors?
Standards
What decision do switches have to make when a frame arrives?
Where to send it next
Is your smartphone a host when you use it to surf the 'Web?
Yes. By definition.
What does Layer 5 standardize?
The application layer standardizes communication between application programs. This includes application messages.
Who owns and manages the servers in IaaSs and SaaSs?
The cloud service provider in both
What devices read Ethernet destination EUI-48 addresses?
The destination host and switches.
What is a route?
The path that a packet takes across an internet from the source host to the destination host.
What devices understand what is really happening?
The router and the source and destination host
How do they make this decision?
Their switching table specifies where to send the frame next, based on the frame's destination address.
What role do access points have in hybrid switched/wireless networks?
They translate between wireless client frames and wired network frames.
What type of port numbers do servers use for common server programs?
Servers use "well-known port numbers." These well-known port numbers have a port number range reserved from port 0 to port 1023. Certain programs are normally on a certain port, like HTTP application programs which are usually on port 80.
What are service level agreements?
Service level agreements (SLAs) are guarantees that the CSP will meet specified service parameters or pay a penalty.
Convert 5.6.7.138 into a 32-bit IP address. (Check Figure: 5 = 00000101) Show a space between each 8-bit segment.
00000101 00000110 00000111 00001100
Convert the following 32-bit binary IP address into DDN 10000000 10101011 00010001 00001101
128.171.17.13
When a packet is transmitted from a source host to a destination host separated by 17 single networks, how many frames will there be?
17
Write 37,400 Mbps properly.
37.4 Gbps
Write 89k bps properly.
89 kbps (needed a space and bps)
What is a CSP? (Do not just spell out the acronym).
A cloud service provider that provides a service opaquely so that customers do not have to worry about the details.
Distinguish between a data link and a route.
A data link is a path a frame takes through a single network A route is the path a packet takes through an internet from the source host to the destination host
What are the three defining characteristics of single networks?
A single networks uses a single technology for transmission. All devices must comply with that technology's standards. There is a controlled address space such that each host address is unique, like a telephone number. Messages in single networks are called frames, not packets.
Why do you need to know what application you are using to know what connection speed you need?
Some applications, such as e-mail, do not need fast connection speeds to be effective. Others, such as video streaming and data backup, do.
Is AWS an IaaS or a SaaS for Netflix?
AWS is an IaaS provider
Name the five layers from bottom to top.
Application Transport Internet Data Link Physical
Give the number for each layer name.
Application (5) Transport (4) Internet (3) Data Link (2) Physical (1)
What is transcoding?
Changing a movie or other video into a form that can be delivered to consumers by Netflix or another streaming services.
What type of port numbers do clients use when they communicate with server programs?
Clients use ephemeral port numbers. Ephemeral port numbers are randomly assigned to a client each time a client initiates or accepts a connection.
What benefits do standards bring?
Competition to lower prices Innovation by vendors to avoid being commodity suppliers Protection in case your product vendor falls behind or even fails
Are frames addressed to the DLL addresses of a switch or the DLL addresses of a destination host?
Destination hosts. Switches merely read the DLL address in the frame in order to pass it on to the destination host with the destination DLL address.
What is fragmentation?
Dividing an (application) message into many smaller parts that will each be sent in a packet or frame.
What is the most widely used single-network address?
EUI-48
If two hosts are on two different single networks, what three problems must be overcome if they are to be able to communicate?
First, the single networks may have different standards. They would not be able to make sense of each other's frames. Second, even if the two networks follow the same standard, this does not mean that they can interoperate. Most fundamentally, a host on one network may have the same DLL address as a host on the other network. Third, how would you link the two networks together? If the link used the standards of one network, it would not connect to the other network for the first two reasons.
What do data link layer (DLL) standards govern?
Frames and switch operation.
What is multiplexing?
Having the packets or frames of multiple users share a physical transmission line.
What is the term we use in networking for any computer attached to a network?
Host
In Figure 2-8, suppose Host A had already sent A6 before it realized that it would need to resend A5. When it then resent A5, A6 would arrive before A5. How would Host B be able to put the information in the two segments back in order?
Host B would look at the sequence numbers A6 and A5 and realize that they were out of order. It would put them in the correct order.
Distinguish between speed to individuals and corporate network speeds.
Speed to individuals is what individual employees experience. Corporate network speeds must be high enough for the aggregate speeds of individual employees.
What type of IP addresses is 32 bits long?
IPv4
What other type of IP address exists, and how long is its addresses?
IPv6, 128 bits
What is the role of ISPs?
ISPs collectively form the core of the Internet, which is also called the Internet's backbone.
Distinguish between IaaS CSPs and SaaS CSPs.
IaaSs provide VMs with operating systems but no application software. SaaSs provide VMs complete with specific application software.
What kind of message does the destination host send if it does not receive a segment during a TCP connection?
If the destination host doesn't receive a segment during a TCP connection, it will send another HTTP request segment. Usually Host A will receive an ACK segment from Host B before Host B sends a HTTP response segment. If Host A doesn't receive an ACK segment after a certain period of time, it will retransmit the HTTP request segment.
What kind of message does the destination host send if it receives a segment that has an error during a TCP connection?
If the destination host receives a segment that has an error during a TCP connection, it will dispose of the segment and send nothing.
In HTTP, can the server transmit if it has not received a request message from the client?
In HTTP, a server can never send a response message unless it has first received a request message from a client.
Describe the four-step handshake in TCP connection closes.
In the four-step handshake, host A will initiate the closing of a connection by sending a FIN segment. Host B will send an ACK segment back to notify Host A that it received the FIN segment. Host B may have more data segments to send so it will send the data after it send the ACK segment. Host A will then send an ACK segment back to Host B to say it got the last data segment. Host B will then send its own FIN segment to end the connection. Host A will then send a final ACK segment back and the connection is closed.
How does fragmentation reduce transmission cost through multiplexing?
Individual users do not have to pay for an entire line; they only pay for the capacity they actually use.
What kind of addresses do hosts have on the Internet?
Internet Protocol (IP addresses)
Why are Internet standards called RFCs?
Internet standards are called request for comments because the Network Working Group team didn't feel like they had authority to call them standards.
What are the advantages of using cloud application programs as a service, compared to traditional application purchasing?
It avoids large one-time expenses in buying software and replaces it with smaller monthly expenses to pay for the service. At least some of the management work is outsourced to the CSP.
Why is layering important for creating standards?
It breaks the standardization job into smaller pieces that can be worked on by specialists in that area.
If the receiver detects an error on the basis of the value in the Frame Check Sequence field, what does it do?
It discards the frame. It does nothing else.
In AWS, what does Netflix manage and not manage?
It does not manage the servers except in the sense of creating, deleting, or moving them. It does manage the applications.
Write 45.6355 kbps properly.
It is written properly.
If someone says that a flag field is set, what does this mean?
It means that the field has a value of 1.
What happens if a service provider fails to meet its SLA?
It must pay a penalty
How does Netflix use the agility offered by Amazon Web Services?
It spins up additional VMs during peak viewing time and tears them down in low viewing periods.
At what layer or layers is PPP a standard?
Layer 2 because it defines frame organization.
At what layer do you find: IP addresses
Layer 3 (internet)
At what layer do you find:packets
Layer 3 (internet)
At what layer do you find:wireless connections
Layers 1 and 2
At which layers are standards defined for single-network technologies?
Layers 1 and 2
What were Ethernet EUI-48 addresses called traditionally?
MAC (media access control) addresses.
Are all single-network addresses EUI-48 addresses?
No.
Does an individual switch know the frame's entire path through a switched single network?
No. Only the next hop.
Are you as a person a host when you use a network?
No. You are not a computer! Always go back to the definition.
How many routes are there when a packet is transmitted?
One
Both single switched networks and routed networks are said to use packet switching. Why is this term confusing?
Packets are always routed Frames are always switched Packets are never switched
What is the name and number of the lowest network standards layer?
Physical layer, Layer 1
What does Layer 1 standardize?
Physical link standards describe transmission media and signaling.
Distinguish between physical links, data links, and routes.
Physical links are connections between adjacent devices on the transmission path. A data link is a path a frame takes through a single network A route is the path a packet takes through an internet from the source host to the destination host
Distinguish between physical servers and virtual machines.
Physical servers are real computers. Virtual machines are parts of a server that act like computers but are not. A physical server may have many virtual machines. VMs can be quickly spun up, spun down, or moved to different physical servers.
In what type of single-network technology is the Point-to-Point (PPP) protocol used?
Point-to-point
On the Internet, what new type of message travels between the source and destination host?
The Internet Protocol (IP) packet
Is the Internet a single network? Explain.
The Internet is not a single network. It is a collection of single networks and smaller internets.
Describe the relationship between cloud computing and networking.
The explosive growth of cloud computing is putting a strain on network capacity.
What is the significance of this depiction for users?
The operation of the Internet should be hidden from them.
What is the purpose of the acknowledgment number field?
The purpose of the acknowledgment number field is to indicate which segment that is being acknowledged.
Describe what happens to a packet between the source and destination host.
The source host places the packet in a frame for the network to the first router Each router along the route receives a frame, removes the packet, and places it into a frame for the next-hop-router The final router delivers the frame to the destination host. The destination host removes the packet from the frame.
What is this decision called when a frame arrives??
The switching decision
What does Layer 4 standardize?
The transport layer does fragmentation on the source host. The transport layer also does reassembly on the destination host.
Why was a new type of address needed for the Internet?
There needed to be an address that would be unique worldwide, unlike data link layer addresses.
Draw a frame in terms of encapsulation, assuming that the frame comes from a contemporary host.
There will be a frame header, followed by the packet, perhaps followed by a frame trailer.
What are frames or packets?
They are small messages that carry application message segments. They travel across an internet (packet) or a single network (frame).
How do content delivery networks reduce streaming delays to customers?
They place a local content server near the user. Either near the user's ISP or within the user's ISP's premises.
How do application programs on different hosts communicate?
They send messages to each other
Why does Netflix make many transcoded versions of each movie?
To serve the particular needs of specific user equipment and network conditions.
List Netflix's content delivery requirements.
Users will not tolerate delay or unreliability
Who funds the Internet?
Users—both individual and corporate
How does the use of virtual clients facilitate file sharing among customers of the system?
Virtual clients can share files with other virtual clients easily.
In this book, do standards and protocols mean the same thing?
Yes, it is very common to see the word protocol in the names of standards.
After a side initiates the close of a connection by sending a FIN segment, will it send any more segments? Explain.
Yes, like I explained in "g" the first FIN segment sent just initiates the Four-Step handshake closing. Host B still has to acknowledge that it got the FIN segment from Host A, and it may even have some more data segments to send to host A. It will send the ACK and Data segments to Host A and Host A will send another ACK segment. Once Host B has got that ACK segment it will send its own FIN segment and Host A acknowledges it by sending one final ACK segment to Host B and the connection is closed.
Is network speed usually measured in bytes per second (Bps) or bits per second (bps)?
bits per second (bps)
